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Nutrient Cycles

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  • 1.
  • 2. NUTRIENT CYCLES: ECOSYSTEM TO ECOSPHERE
    • Nutrient cycling occurs at the local level through the action of the biota.
    • Nutrient cycling occurs at the global level through geological processes, such as, atmospheric circulation, erosion and weathering.
  • 3. NUTRIENT CYCLES
    • The atoms of earth and life are the same; they just find themselves in different places at different times.
    • Most of the calcium in your bones came from cows, who got it from corn, which took it from rocks that were once formed in the sea.
    • The path atoms take from the living (biotic) to the non-living (abiotic) world and back again is called a biogeochemical cycle .
  • 4. Nutrients: The Elements of Life
    • Of the 50 to 70 atoms (elements) that are found in living things, only 15 or so account for the major portion of living biomass.
    • Only around half of these 15 have been studied extensively as they travel through ecosystems or circulate on a global scale.
  • 5. A GENERALIZED MODEL OF NUTRIENT CYCLING IN AN ECOSYSTEM
    • The cycling of nutrients in an ecosystem are interlinked by an a number of processes that move atoms from and through organisms and to and from the atmosphere, soil and/or rocks, and water.
    • Nutrients can flow between these compartments along a variety of pathways.
  • 6. Nutrient Compartments in a Terrestrial Ecosystem
    • The organic compartment consists of the living organisms and their detritus.
    • The available-nutrient compartment consists of nutrients held to surface of soil particles or in solution.
    • The third compartment consists of nutrients held in soils or rocks that are unavailable to living organisms.
    • The fourth compartment is the air which can be found in the atmosphere or in the ground.
  • 7. Uptake of Inorganic Nutrients from the Soil
    • With the exception of CO 2 and O 2 which enter though leaves, the main path of all other nutrients is from the soil through the roots of producers.
    • Even consumers which find Ca, P, S and other elements in the water they drink, obtain the majority of these nutrients either directly or indirectly from producers.
  • 8. The Atmosphere Is a Source of Inorganic Nutrients
    • The atmosphere acts as a reservoir for carbon dioxide (CO 2 ), oxygen (O 2 ) and water (H 2 O).
    • These inorganic compounds can be exchanged directly with the biota through the processes of photosynthesis and respiration.
    • The most abundant gas in the atmosphere is nitrogen (N 2 );about 80% by volume. Its entry into and exit from the biota is through bacteria.
  • 9. Some Processes By Which Nutrients Are Recycled
    • Cycling within an ecosystem involves a number of processes.
    • These are best considered by focusing attention on specific nutrients.
  • 10. CARBON, HYDROGEN AND OXYGEN CYCLES IN ECOSYSTEMS
    • C, H & O basic elements of life; making up from about 98% of plant biomass.
    • CO 2 and O 2 enter biota from the atmosphere.
    • Producers convert CO 2 and H 2 O into carbohydrates (C H 2 O compounds) and release O 2 from water.
    • Producers, consumers and decomposers convert C H 2 O compounds, using O 2 , back into CO 2 and H 2 O .
  • 11. CARBON, HYDROGEN AND OXYGEN CYCLES IN ECOSYSTEMS
    • Carbon and oxygen cycle come out of the air as carbon dioxide during photosynthesis and are returned during respiration.
    • Oxygen is produced from water during photosynthesis and combines with the hydrogen to form water during respiration.
  • 12. PHOSPHOROUS CYCLE IN ECOSYSTEMS
    • Phosphorus, as phosphate (PO 4 -3 ), is an essential element of life.
    • It does not cycle through atmosphere, thus enters producers through the soil and is cycled locally through producers, consumers and decomposers.
    • Generally, small local losses by leaching are balanced by gains from the weathering of rocks.
    • Over very long time periods (geological time) phosphorus follows a sedimentary cycle.
  • 13. NITROGEN CYCLE IN ECOSYSTEMS
    • Nitrogen (N 2 ) makes up 78% of the atmosphere.
    • Most living things, however, can not use atmospheric nitrogen to make amino-acids and other nitrogen containing compounds.
    • They are dependent on nitrogen fixing bacteria to convert N 2 into NH 3 (NH 4 + ).
  • 14. Sources of Nitrogen to the Soil
    • Natural ecosystems receive their soil nitrogen through biological fixation and atmospheric deposition.
    • Agricultural ecosystems receive additional nitrogen through fertilizer addition.
  • 15. Biological Sources of Soil Nitrogen
    • Only a few species of bacteria and cyanobacteria are capable of nitrogen fixation.
    • Some are fee-living and others form mutualistic associations with plants.
    • A few are lichens.
  • 16. Atmospheric Sources of Soil Nitrogen
    • Lightning was the major source of soil nitrogen until recent times when the burning of fossil fuels became a major source of atmospheric deposition.
    • Nitrogen oxides come from a variety of combustion sources that use fossil fuels. In urban areas, at least half of these pollutants come cars and other vehicles.
  • 17. Agricultural Supplements to Soil Nitrogen
    • Various forms of commercial fertilizer are added to agricultural fields to supplement the nitrogen lost through plant harvest.
    • Crop rotation with legumes such as soybeans or alfalfa is also practiced to supplement soil nitrogen.
  • 18. Biological Nitrogen Fixation
    • Nitrogen fixation is the largest source of soil nitrogen in natural ecosystems.
    • Free-living soil bacteria and cyanobacteria (blue-green “algae”) are capable of converting N 2 into ammonia (NH 3 ) and ammonium (NH 4 + ).
    • Symbiotic bacteria (Rhizobium ) in the nodules of legumes and certain other plants can also fix nitrogen.
  • 19. Nitrification
    • Several species of bacteria can convert ammonium (NH 4 + ) into nitrites (NO 2 - ).
    • Other bacterial species convert nitrites (NO 2 - ) to nitrates (NO 3 - ).
  • 20. Uptake of Nitrogen by Plants
    • Plants can take in either ammonium (NH 4 + ) or nitrates (NO 3 - ) and make amino acids or nucleic acids.
    • These molecules are the building blocks of proteins and DNA, RNA, ATP, NADP, respectively.
    • These building blocks of life are passed on to other trophic levels through consumption and decomposition.
  • 21. Ammonification
    • Decomposers convert organic nitrogen (CHON) into ammonia (NH 3 ) and ammonium (NH 4 + ).
    • A large number of species of bacteria and fungi are capable of converting organic molecules into ammonia.
  • 22. Denitrification
    • A broad range of bacterial species can convert nitrites, nitrates and nitrous oxides into molecular nitrogen (N 2 ).
    • They do this under anaerobic conditions as a means of obtaining oxygen (O 2 ).
    • Thus, the recycling of N is complete.
  • 23. NITROGEN CYCLE IN ECOSYSTEMS
    • Molecular nitrogen in the air can be fixed into ammonia by a few species of prokaryotes.
    • Other bacterial species convert NH 4 - into NO 2 - and others to N0 3 - .
    • Producers can take up NH 4 - and to N0 3 - use it to make CHON.
    • Decomposers use CHON and produce NH 4 - .
    • Recycling is complete when still other species convert N0 3 - and NO 2 - into N 2 .
  • 24. NUTRIENT LOSS IN ECOSYSTEMS I
    • The role of vegetation in nutrient cycles is clearly seen in clear cut experiments at Hubbard Brook.
    • When all vegetation was cut from a 38-acre watershed, the output of water and loss of nutrients increased; 60 fold for nitrates, and at least 10 fold for other nutrients.
    • Freeman describes the experiments on page 1254 and in Figure 54.15.
  • 25. NUTRIENT LOSS IN ECOSYSTEMS II
  • 26. NUTRIENT LOSS IN ECOSYSTEMS III
  • 27. GLOBAL NUTRIENT CYCLES
    • The loss of nutrients from one ecosystem means a gain for another. (Remember the law of conservation of matter.)
    • When ecosystems become linked in this manor, attention shifts to a global scale. One is now considering the ECOSPHERE or the whole of planet earth.
  • 28. GLOBAL WATER CYCLE I
    • Water is the solvent in which all the chemistry of life takes place and the source of its hydrogen.
    • The earth’s oceans, ice caps, glaciers, lakes, rivers, soils and atmosphere contains about 1.5 billion cubic kilometers of H 2 O.
    • It has been estimated that all the earth’s water is split by plant cells and reconstituted by the biota about every 2,000,000 years .
  • 29. GLOBAL WATER CYCLE II
    • Oceans contain a little less than 98% of the earth’s water.
    • Around 1.8% is ice; found in the two polar ice caps and mountain glaciers.
    • Only 0.5% is found in the water table and ground water.
    • The atmosphere contains only 0.001% of the earth’s water, but is the major driver of weather.
  • 30. GLOBAL WATER CYCLE III
    • The rate at which water cycles is shown in Figure 54.16 (Freeman, 2005).
    • Evaporation exceeds precipitation over the oceans; thus there is a net movement of water to the land.
    • Nearly 60% of the precipitation that falls on land is either evaporated or transpired by plants; the remainder is runoff and ground water.
  • 31. GLOBAL WATER CYCLE IV
  • 32. GLOBAL CARBON CYCLE I
    • All but a small portion of the earth’s carbon (C) is tied up in sedimentary rocks; but the portion that circulates is what sustains life.
    • The active pool of carbon is estimated to be around 40,000 gigatons.
    • 93.2 % found in the ocean; 3.7% in soils; 1.7% in atmosphere; 1.4% in vegetation.
  • 33. GLOBAL CARBON CYCLE II
    • The rate at which the biota exchanges CO 2 with atmosphere has been estimated to be every 300 years.
    • The rate at which carbon cycles through various components of the ecosphere is summarized in Figure 54.17 in Freeman (2005).
    • Since the industrial revolution, a new source of stored sedimentary carbon has been added to the atmosphere from the burning of fossil fuels causing a concern with respect to climate change.
  • 34. GLOBAL CARBON CYCLE III
  • 35. GLOBAL NITROGEN CYCLE I
    • 99.4% of exchangeable N is found in the atmosphere; 0.5% is dissolved in the ocean; 0.04% in detritus ; 0.006% as inorganic N sources; 0.0004% in living biota.
    • Figure 54.19 in Freeman (2005) gives major pathways and rates of exchange.
  • 36. GLOBAL NITROGEN CYCLE II
    • Humans are adding large amounts of N to ecosystems. Some estimates of are given in Figure 54.20 in Freeman (2005).
    • Among the fossil fuel sources, power plants and automobiles are important sources of atmospheric nitrogen deposition in the US.
    • Investigations of native plant and natural ecosystem responses to nitrogen deposition and global warming will be a focus of study.
  • 37. GLOBAL NITROGEN CYCLE III

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